Tightly adhered silk fibroin coatings on Ti6Al4V biometals for improved wettability and compatible mechanical properties

Abstract

Medical titanium alloys remain the most successful commercial bone implant material, but efforts are demanded to improve the biocompatibility. Silk fibroin (SF) is a natural structural protein with tunable mechanical properties and biocompatibility. Herein we established a facile method of physical depositing SF coatings via HFIP solvent onto Ti6Al4V (TC4) biometals. To stabilize SF coatings, ethanol induced physical crosslinking and EGDE chemical crosslinking was applied. The coating-substrate system revealed tightly integrated interface between SF and TC4. Importantly, the introduction of SF coatings significantly increased the water wettability of the TC4 surface by decreasing the water contact angle from 93° to 67°. Furthermore, the interfacial bonding strength, measured by advanced centrifugal measurement, was affected by the surface roughness of the substrate in a parabolic fashion and the bonding strength increased with reduced thickness of the coating. An appropriate roughness was optimized at Ra~1 μm and 7 MPa adhesion strength was achieved. Cytotoxicity using L929 cell line and cell viability and cytoskeleton organization using MG63 cell line of the SF-TC4 hybrid were investigated. The study provides a facile way of physical deposition of biopolymer coatings on inert medical metals as well as a basis for further improving the adherence of biometals and polymers. Keywords: Metal-polymer interface, Surface roughness, Structural protein, Biocompatibility, Adhesion strength, Bone tissue engineering